This disclosure generally relates to a display film stack for back lighting of flat panel display systems, and a method of modeling a display film stack to enhance on-axis luminance.
Display films are used in a variety of applications, such as part of displays or lighting devices. Regardless of the application, display films can be used to improve the efficiency of the light transmitted from a light source to an output by redirecting the light.
One technology that has gained attention in display technologies is liquid crystal (LC) technology. An LC display (LCD) includes a liquid crystal material that is modulated to provide a light-valve function. In many LCD applications, it is useful to improve the power efficiency. Increasing the power efficiency of an LCD (or other similar display) can be useful in improving the image quality of the display, among other benefits.
Conventional LCD backlights for large displays have conventionally employed multiple lamps to provide sufficient brightness over a large area. Typically, these directly illuminated backlights are used for television and large display applications and contain linear arrays of fluorescent lamps with reflectors. In order to provide a uniform intensity profile from the surface of the backlight before passing through the LCD panel, display film(s) are used to “spread-out” or diffuse the light from the linear array of fluorescent lights so as to eliminate the visibility of linear “hot spots” or non-uniformities in the backlight luminance. Such a display film can include a surface texture to aid in the diffusion. This surface texture can be shaped and arranged to redirect light in an LCD, making the LCD more energy efficient.
Light collimating capability and the overall light efficiency are important components of any display system. Both of these factors, however, are affected by the surface texture of the display film as well as the refractive index of the material used to make the display film.
A conventional display film stack used for back lighting of flat panel displays can include a bottom diffuser to diffuse the input light and hide the lamps or reflective paint dots underneath the display film stack, and a prismatic film to collimate the light from the bottom diffuser of the display film stack to gain on-axis luminance. Examples of prismatic films include BEF made by 3M Company, and the like. Examples of diffuser films include D121 made by Tsujiden Company Ltd. of Japan, UTE II made by MNTech Company of Korea, PTR733 made by Shinwha Intertek Company of Korea, BE2039 made by General Electric®, and the like.
It is desirable to have a multiple-film stack that is optimally designed to better balance both the light collimating ability and the overall light efficiency of the stack to enhance the on-axis luminance of the backlight system.